Lubricating oil compositions for use in crankcase engine oils comprise a major amount of base stock oil and minor amounts of additives that improve the performance and increase the useful life of the lubricant. Crankcase lubricating oil compositions conventionally contain basic metal complexes, which act as detergents and acid neutralizers, phenolic and/or aminic antioxidants and organic friction modifiers containing at least one hydroxyl or amino group, which function as organic friction modifiers that are effective in improving fuel economy. In the face of increased demands for improved fuel economy, and further demands for reductions in the amounts of metal (ash) contained in the lubricant, formulators have used ever-increasing amounts of organic friction modifiers.
Lubricating oil additives are commonly provided to lubricant formulators in the form of 10 to 80 mass %, e.g., 20 to 80 mass % active ingredient (AI) concentrates, which are then dissolved in major amounts of oil of lubricating viscosity to provide a fully formulated lubricant. The concentrates are commonly diluted in 3 to 100, e.g., 5 to 40 parts by weight of oil of lubricating viscosity, per part by weight of the additive concentrate. As noted above, certain lubricating oil additives are known to interact with others in concentrates. One such known interaction occurs between organic friction modifiers and overbased metal detergents. Specifically, the organic friction modifiers have been found to adversely affect the complex of the metal detergents, causing the formation of sediment in the concentrate upon storage. Previously, this interaction has been minimized by selecting detergents that did not severely interact with the organic friction modifier. The addition of a polyalkenyl acylating agent has also been found to regulate this unwanted interaction. However, the detergents less likely to interact with organic friction modifiers have been found to cause gelation problems in additive packages, and the presence of polyalkenyl acylating agents (e.g., polyisobutenyl succinic anhydride (PIBSA)) has been found to negatively impact the fuel economy potential of lubricating oil compositions. Further, with the increased amounts of the organic friction modifier now required, the effect of polyalkenyl acylating agent compatibilizers and detergent selection on additive package stability has become insufficient.
As lubricating oil quality standards have become more stringent, the required amount of organic friction modifier has increased, and the presence of even minor amounts of sediment in additive concentrates has become unacceptable to lubricant formulators. Therefore, it would be advantageous to be able to provide additive concentrates containing overbased metal detergents and high levels of organic friction modifiers, in which the components do not interact to form sediment.